Heritability of daytime cortisol levels and cortisol reactivity in children.
Individuals differ widely in cortisol output over the day and cortisol reactivity to challenge, both of which are relevant to disease risk. There is limited evidence concerning the heritability of these differences, so we evaluated the heritability of cortisol levels in the afternoon and cortisol reactivity using a twin design. The study involved 80 monozygotic (MZ) and 70 dizygotic (DZ) same-sex twin pairs aged 11.2 years on average. Salivary cortisol was measured in the afternoon at home before and after playing a computer game. Ratings of excitement and upset were also obtained, and objective task performance was assessed. Salivary cortisol levels averaged 4.08 (S.D. 2.3) nmol/l at pretask baseline, and declined on average over the session to 3.45 (1.9) nmol/l immediately after the tasks and 2.87 (1.6) nmol/l 10min later. There were, however, marked individual differences, with cortisol reactivity (difference between pretask baseline and post-task 1) ranging from +4.53 to -6.23nmol/l. Intra-class correlations for all the cortisol parameters were substantially greater for MZ (range 0.41-0.57) than for DZ (0.11-0.29) twin pairs. Quantitative genetic modelling confirmed significant heritability for pretask baseline cortisol (58%), the two post-task values (60 and 56%), and cortisol reactivity (44%). The study lacked power for assessing sex differences. Subjective reports of excitement were also somewhat heritable, but there was little covariation of cortisol and subjective responses, so genetic influences on covariation could not be tested. These findings indicate that individual differences in children's cortisol levels recorded before tasks and cortisol reactivity to behavioural challenges are influenced by genetic factors.
Steptoe
Andrew
A
Psychobiology Group, Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London, UK. Electronic address: a.steptoe@ucl.ac.uk.
van Jaarsveld
Cornelia H M
CHM
Centre for Health Behaviour Research, Department of Epidemiology and Public Health, University College London, London, UK.
Semmler
Claudia
C
Centre for Health Behaviour Research, Department of Epidemiology and Public Health, University College London, London, UK.
Plomin
Robert
R
Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, London, UK.
Wardle
Jane
J
Centre for Health Behaviour Research, Department of Epidemiology and Public Health, University College London, London, UK.
D002648:Child; D002940:Circadian Rhythm; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007206:Individuality; D008297:Male; D011595:Psychomotor Agitation; D019655:Quantitative Trait, Heritable; D012463:Saliva / Q000378:metabolism*; D014429:Twins, Dizygotic / Q000378:metabolism; D014430:Twins, Monozygotic / Q000378:metabolism
D006854:Hydrocortisone